Spring is the time of the year when birds sing but when you go far to the Northern Hemisphere, beneath the ice, another lesser-known concert is just coming to an end and it was by bowhead whales.
A University of Washington study has recorded sounds from bowhead whales, to discover that these marine mammals have a surprisingly diverse, constantly shifting vocal repertoire. The researchers analyzed audio recordings gathered year-round east of Greenland.
The bowhead whales had been frequently hunted almost to extinction in the 1600s and was recently estimated at about 200 animals. Audio recordings gathered from 2010 to 2014 show that there is a healthy population of them as they have recorded about 184 different songs.
"If humpback whale song is like classical music, bowheads are jazz," said lead author Kate Stafford, an oceanographer. "The sound is more freeform. And when we looked through four winters of acoustic data, not only were there never any song types repeated between years, but each season had a new set of songs."
Stafford has recorded whales’ sounds throughout the world’s oceans and she first detected bowhead whales singing off the other side of Greenland in 2007. Another study by Stafford of the Spitsbergen whales off west Greenland reported in 2012 that the whales were singing continuously during the winter breeding season, which means there may be a healthy population of them in that area.
"We were hoping when we put the hydrophone out that we might hear a few sounds," Stafford said about their earlier study. "When we heard, it was astonishing: Bowhead whales were singing loudly, 24 hours a day, from November until April. And they were singing many, many different songs."
The hydrophones, which are underwater microphones, picked up slightly more singing in the later years of the study and more surprisingly, there was a relentless variety in the animals’ songs.
The only other whale that sings elaborate songs are humpback whales found off Hawaii and Mexico waters. The humpback’s each population debuts a new tune in the spring."Now this data confirms that bowhead whale songs are completely different from the humpbacks’."
"Why are they changing their songs so much? In terms of behavioral ecology, it’s this great mystery," explains Stafford.
The study was published in Biology Letters, a journal of the United Kingdom’s Royal Society.
A bowhead whale surfaces in Fram Strait, to the northwest of Norway (CREDIT: Kit Kovacs/Norwegian Polar Institute)